Another rotor break off in flight
 

Seems that this was in Korea. What type helicopter is that?

KAI Surion

https://en.m.wikipedia.org/wiki/KAI_KUH-1_Surion

Looks like a...

KAI KUH-1 Surion

"As the prime sub-contractor, Eurocopter has provided technical assistance in part for developing the power transmission, main gearbox, boom and tail gearboxes, automatic flight control system and rotor mast."
Just saying...

Regards.
Aser

Related development......332. Per that amazingly always accurate source....Wikipedia.

Sound familiar?

MUH-1 Marineon, a Surion variant.

Thats the mast snapping/separating at the head, rather than a gearbox internal failure ?

If you try to slow the video, or advance slowly, it seems as the coning angle is all over the place on takeoff. First it may appear normal, but seems to vary, then right around 9 seconds, when just over the last building, you can see the rotor tilt left, to the camera, then back forward. Then the cone angle drops, and raises again, before the rotor drops a lot around 10 seconds, one frame seems like blades are crowded in the front, spreads out flat again and one blade departs. The two other puma departures had intact heads and blades. I would not rule out a gearbox seizure as some have speculated, but probably not my first guess. But since this event was takeoff rather than cruise, all control positions and airflow vastly different, so the subsequent chain events could be different. Still, usually rotor heads and the blade roots tend to stay grouped, even after powered impact. This blade is missing at the head altogether, so I would suspect a blade attachment, or at least a blade control mechanism that could send this to extreme pitch, that would produce an extremely high load in the flatwise direction rather than chordwise, before separation. Who has graphics of rotor/ control system? Assume they are same as the AS332.

Except for the blade departure, clear in a 0.25x reproduction, I really need to check my glasses or get a bigger screen.

Looks like leading edge pitch control horns. If the mast or transmission let go, the blade roots would rise up while the pitch links remain at the same point.
This would produce a brief period of low or even negative pitch. Kind of matches the footage at the 10 sec mark when the coning angle of the rotor disk goes negative.
I think the missing red blade flapped down enough to contact the fuselage and sheared off at the hub.

MGB - same as 225
 

The Surion fleet has only recently returned to flight following a prolonged grounding due to the Norwegian 225 accident. They share a common MGB. This is terrible news.
RIP to those departed.

There was a big change in tail rotor rpm also. I'm going cross-eyed trying to tell if it was immediately before or simultaneous with the main rotor breakup/ separation.
Looks like first a rotor blade took out the windscreen with a simultaneous drop in TR rpm, then rapidly followed by main rotor separation.

The cone angle definitely goes very suddenly negative just before the break up, for me thats the cause. So perhaps a collective control link problem?

I have NEVER seen a MR Mast shear off like that!!! I also see a very abrupt change in RPM at 17 sec.

While you Video Geeks are examining the video....consider the actions of the entire rotor system immediately prior to the apparent separation of the one blade from the Rotor Head if you will.

I am wondering how the Rotor System would react to a sudden stoppage of the MGB particularly in the way each Blade would react both individually and as an attached part of the whole Rotor Head.

If the MGB seized and the Mast sheared off.....that would also shear the Pitch Change Links I am thinking.

As that happens very quickly....the effect on the Rotor Blade movements would also be very rapid and should (I am guessing) transmit a somewhat common reaction to all of the Blades.

Meaning to me....the Rotor Head would act more or less in a common manner and not shed individual blades.

If that Rotor Head moved such that a single blade made contact with a strong object (say the fuselage) then I can see a single blade being lost from the Head.

Do you see the whole Rotor Head Tip Path Plane tilting in such a manner or are we seeing a single blade launching off for points unknown while the rest of the blades act in a common manner?